1. Field of the Invention
The present invention relates to a fluorescent lamp.
2. Description of the Related Art
So far, this type of the fluorescent lamp is configured as shown below in order to protect clothing and printed matters from fading due to ultraviolet light.
An ultraviolet suppressing film made of titanium oxide (TiO.sub.2) is formed in a bulb and a phosphor film is laminated on the internal surface of the ultraviolet absorbing film or the surface at the discharge space side.
As the result, the ultraviolet light (with the wavelength of approx. 365 nm) produced in the discharge space is interrupted by said ultraviolet suppressing film. Therefore, it is not emitted from the bulb.
This type of the fluorescent lamp is made by the following process.
First, a cleaned bulb is hung by setting the bulb axis vertically. The ultraviolet suppressing material mixture in which titanium-oxide particles are melted is poured into the bulb from the top of the hung bulb.
After the ultraviolet suppressing material mixture is formed on the entire inner surface of the bulb, it is dried by hot air.
Then, the ultraviolet suppressing material mixture is baked in a baking oven to form an ultraviolet absorbing film on the inner surface of the bulb.
And, the phosphor mixture mixed with fluorescent materials to emit three bands of R (red), G (green), and B (blue) is poured onto the inner surface of the ultraviolet suppressing film formed in the bulb from the top of the bulb. Then, the phosphor mixture is dried by hot air. And, the phosphor mixture is baked in the baking oven to laminate phosphor film on the inner surface of the ultraviolet suppressing film.
However, the fluorescent lamp made by the abovementioned process has the following problem because the ultraviolet suppressing film also suppresses visible radiation.
That is, when the thickness of the ultraviolet suppressing film is increased in order to adequately suppress ultraviolet light, the light output (lumen) of the fluorescent lamp decreases because more visible radiation is suppressed. On the contrary, when the thickness of the ultraviolet suppressing film is decreased to prevent the light output of the fluorescent lamp from decreasing, ultraviolet light is inadequately suppressed.